FLIGHT
ROLLS-ROYCE MERLIJS
WITH the advent of the new Series 130 it can truth-fully be said that the Merlin has carried progres-sive development of a basic type farther than any
other aircraft engine in'the world, for within a period of
lea years (the first Merlin was produced in 1936), not only
has its power output been increased from less than 1,000
to more than 2,000 b.h.p., but, in addition, more Merlins
have been built than any other type.
The Merlin 130 and 131 are specially developed variants
of the Series 100 engines, and have been specifically pre-
pared for installation in the de Havilland Hornet, which
is the first twin-engined British aircraft to have handed
airscrews. This feature accounts for the designation 130
and 131, the former being a right-hand tractor unit for
the port side, and the latter a left-hand tractor for. the
starboard nacelle. As the airscrew on the 130 rotates in
the opposite direction to that of the 131, it might at first
sight appear that this would involve considerable comph-
cation, and that it would be necessary for the crankshaft
to rotate in the opposite direction—making the engine
"handed" throughout. This, however, is not the case;
all that is necessary on a liquid-cooled, in-line engine em-
ploying a single spur reduc- •
tion gear is the introduction
of an idler wheel between the
driving pinion and the main
gear wheel. The advantage
of this simple modification,
which is clearly shown in an
illustration, is that the two
engines have 95 per cent, of
spares in common, and to
alter the engine from one
" hand " io the other, it is
only necessary to change the
reduction gear ; the weight in-
crease with the additional
gear and bearings is prac-
tically negligible and can be
discounted.
Although the Merlin 100s
were the first of a new series
of two - stage, two - speed,"
inter cooled types incorporat-
ing many improved features,
the series 130 and 131 have further new features which
enable an improved installation to be effected for fighter
aircraft. In fact, it would not be inapt to describe
this latest Merlin as being "tailored" to suit the particu-
lar installation; this has resulted in a very low frontal
area per b.h.p. An illustration gives a curve of interesting
comparisons of frontal-area : power, starting with the Eagle
produced at the beginning of the first World War and end-
ing with the Merlin 130 of to-day. From this curve it
will be seen that a steady increase in power per square
foot of frontal area was achieved during the inter-war
years, every four years producing an increase of roughly
25 b.h.p./sq. ft., until 1936, and then, with the advent of
the Merlin, there was a considerable improvement amount-
ing progressively to 60 b.h.p./sq. ft. in 1940; 100 b.h.p./
sq. ft. between 1940 and 1944, until in 1945 the amazing
figure of 340 b.h.p. /sq. ft. was achieved with the Merlin
IOOS.
History of Collaboration
The Hornet is a good example of the excellence which
can be obtained1 when close collaboration exists between
Cf
\
a:
3OO
275
2SO
22S
2OO
175
ISO
125
CO
75
SO
25
CONDOR -
I92O 1922 B2*626
KESTREL
S55
VULTURE
"MERLIN
B34 1936 I95T
B.H.P./SQFT. OF FRONTAL AREA
The Merlin 131 differs from the 130
only in that an idler wheel is inter-
posed between the driving pinion and .
the main gear wheel.
the aircraft designer and the engine
manufacturer, although sound basic
design must obviously be the founda-
tion if extensive developments are
planned. In .this connection, when
the design for the Mosquito was lakL-flL
down in 1939/40, the decision was
taken to use Merlin 20s, as they were
then sufficiently advanced in design
and development to ensure that the
Mosquito would have a superior per-
lormance to that of any equivalent
enemy aircraft. Further, it was pre-
dicted by Rolls-Royce that the Mer-
lin 20 would be capable of much
greater development, and thin would
ensure the initial superiority being re-
tained over a period of years.
Even the most casual survey of the
Mosquito's record is sufficient to illus-
trate how well this long-term planning
has succeeded, andiit is sufficient to